The present invention relates to broadband underwater acoustic transducers which are essentially used as acoustic signal emitters in the active sonars of surface vessels. However, these transducers may also be used as receivers, and also in sonars for submarines.
It is known that with progress in sonars, one seeks to decrease the working frequency, so as among other things to increase the range of these sonars, and the emission power. One also seeks to have transducers which operate in broadband so as to be able, through suitable processing, to circumvent the phenomena of reverberation, and to be able to use several sonars in one and the same geographical zone, thereby achieving interoperability of systems.
At present the most commonly used emitter transducers are of the so-called xe2x80x9ctonpilzxe2x80x9d type. These transducers use an emitter horn which is excited by a ceramic pillar which bears on a countermass.
These xe2x80x9ctonpilzxe2x80x9d emitters make it possible to obtain a good level of emission and considerable back rejection, allowing channel formation with a low level of secondaries. Furthermore, they are usable both for emission and for reception.
On the other hand they exhibit the disadvantage of having a relatively small bandwidth, typically corresponding to a quality factor Q≅3.5. Moreover the transducer/casing join is relatively fragile, giving rise to a risk of water ingress at this level. Finally, since the frequencies which can be emitted are strictly related to the dimensions of the horn, it is only possible to drop down in frequency by increasing these dimensions, this rapidly becoming prohibitive.
To alleviate these drawbacks, the invention proposes a broadband underwater acoustic transducer, comprising at least one piezoelectric plate operating in flexion, principally characterized in that it furthermore comprises a cylindrical cap closed at one end by a baseboard and open at the other end so as to form a first cavity; the piezoelectric plate being fixed on the outside face of the baseboard and the first cavity of the cap being open freely toward the outside medium in which the cap is immersed.
According to another characteristic, the cross section of the cap is circular.
According to another characteristic, the cross section of the cap is elliptical.
According to another characteristic, the first cavity is filled at least partially with a matching material whose acoustic characteristics are different from those of the outside medium in which the transducer is immersed.
According to another characteristic it furthermore comprises a body including a second inside cavity closed by the cap in such a way as to be insulated from the outside medium with the piezoelectric plate enclosed in the second inside cavity and the first cavity pointing outward.
According to another characteristic, it comprises two cap/piezoelectric plate assemblies fixed together head-to-tail.
According to another characteristic, the cap forms the front face of a transducer of the so-called xe2x80x9ctonpilzxe2x80x9d type.